Because of having properties suited for use as engineering plastics, for example, excellent mechanical properties such as rigidity and toughness as well as excellent thermal properties, a polyamide has widely been used in applications such as electric and electronic components, machine components, and automobile components, centering on injection molding applications. There has been known, as a method of further improving toughness of a polyamide resin, a method of mixing an olefin-based elastomer, or a core-shell compound obtained by coating a rubbery core layer with a shell layer of a glassy resin. There has been proposed, as technology of mixing the olefin-based elastomer, for example, a polyamide-based resin composition comprising a continuous phase composed of a polyamide resin, and a particle-like dispersion phase composed of a polyolefin modified with an α,β-unsaturated carboxylic acid dispersed in the continuous phase (see, for example, Patent Literature 1). There have been proposed, as technology of mixing the core-shell compound, for example, mixing an impact-resistant thermoplastic resin composition comprising a composite rubber-based graft copolymer and a thermoplastic resin, the composite rubber-based graft copolymer being obtained by graft polymerization of multi-layered structure polymer particles comprising a polyalkyl (meth)acrylate as a core, and a first layer composed of a polyorganosiloxane and a second layer composed of a polyalkyl (meth)acrylate formed on the core with a vinyl-based monomer (see, for example, Patent Literature 2); and mixing a polyamide resin composition comprising a polyamide resin including a dicarboxylic acid unit containing a terephthalic acid unit, a 1,9-nonanediamine unit and/or a diamine unit containing a 2-methyl-1,8-octanediamine unit, and resin fine particles having a core-shell structure (see, for example, Patent Literature 3). When these resin compositions are applied for various applications, particularly automobile structural materials, it becomes necessary to satisfy both toughness and rigidity. The resin compositions disclosed in Patent Literatures 1 to 3 had a problem that rigidity deteriorates, although mixing of the olefin-based elastomer or the core-shell compound leads to an improvement in impact resistance or toughness.
Meanwhile, there have been proposed, as a method of improving impact strength and toughness, for example, a resin composition obtained by reacting a polyolefin modified with an unsaturated carboxylic anhydride with a polyrotaxane having a functional group (see, for example, Patent Literature 4); and a polylactic acid-based resin composition comprising a polyrotaxane in which the opening part of a cyclic molecule having a graft chain composed of polylactic acid is included by a linear molecule (see, for example, Patent Literature 5).